Today, denim products have been much popular, as pants, trousers and/or jackets. These denim products are made of thick cotton fabrics whose warps are dark blue and whose wefts are white and which are of diagonal weave or plain weave. There are generally two methods for producing design patterns on these denim products, one of which is a chemical washing method in which said denim products are put into a drum cage and a specified quantity of pumice which has been immersed and seasoned in hypochlorous acid calcium water is put in said drum cage altogether and marble-like spotted design patterns can be produced by aid of rubbing and friction between said denim woven products and said pumice by rotating said denim woven products together said pumice in said rotary drum cage, and the other of which is called a chemical bleaching method in which said denim woven products are agitated for a specified period of time in water solution whose hypochlorous acid calcium density is about 6%, thereby causing said denim woven products to be totally white-bleached.